docs: def iter_annotation_value_pairs(graph) -> Iterable[Tuple[str, str]]:
      """Iterate over the key/value pairs, with duplicates, for each annotation used in a BEL graph.
  
      :param pybel.BELGraph graph: A BEL graph
      """
      return (
          (key, value)
          for _, _, data in graph.edges(data=True)
          if ANNOTATIONS in data
          for key, values in data[ANNOTATIONS].items()
          for value in values
      )